B
I wish you had seen this film before.
I wish I had done it for you before.
I wish I had visited this museum.
I wish I had been there before.
I wish they had staged this performance before.

C
If you had chosen this room you would have watched TV.
If you had investigated this problem you would have answered this question.
If he had measured the temperature he would have explained the phenomenon.
If they had unified the facts they would have proved the problem.
If they had processed the data they would have had the results.